This invention relates to a variable displacement pump arranged to supply a hydraulic fluid to sliding portions and so on of an internal combustion engine for a vehicle.
U.S. Patent Application Publication No. 2009/0285707 A1 (corresponding to Internal Publication Number WO 2008/003169 A1) discloses a vane type variable displacement oil pump. This variable displacement oil pump includes a first spring arranged to urge a cam ring in a direction (hereinafter, referred to as an eccentric direction) to increase an eccentric amount of the cam ring with respect to a center of a rotation of a rotor, a second spring arranged to urge the cam ring in the eccentric direction when the eccentric amount of the cam ring becomes equal to or smaller than a predetermined amount, and a control hydraulic chamber separated between a pump housing and the cam ring. This variable displacement pump is arranged to control the eccentric amount of the cam ring by urging forces of the first spring and the second spring, and a discharge pressure which is introduced into the control hydraulic chamber, and which is acted to urge the cam ring in a concentric direction (opposite to the eccentric direction) against the spring forces of the first and second springs, and thereby to vary the discharge amount.
When the discharge pressure of the pump becomes equal to a first predetermined hydraulic pressure by the increase of the engine, the cam ring is moved in the concentric direction against the spring force of the first spring until the cam ring is abutted on the second spring. Then, when the discharge pressure of the pump becomes equal to a second predetermined hydraulic pressure by the further increase of the engine speed, the cam ring is further moved in the concentric direction against the spring forces of the first and second springs.